The present invention relates to an air bag device, more particularly, to an air bag device which can prevent an occupant from bumping against a steering wheel, absorb an impact force applied to the occupant's head and chest and reliably protect the occupant.
Recently, an air bag device is adopted to various kinds of vehicles as a passive occupant protection system for efficiently protecting an occupant from the action of the impact force at a collision.
The purpose of the air bag device is to prevent the occupant from a secondary collision in a cabin by receiving the occupant's body, particularly, the head and chest with a bag shaped cushion filled with gas during a collision.
As shown in FIG. 1, when a position D1 of an occupant in a driver's seat moves to the position D2 at a collision, the occupant is protected by the deployed air bag 54 at his chest and head. Thereby, the occupant is protected from the secondary collision, that is, the occupant plunges into and bumps against a steering wheel or a windshield of the vehicle.
As shown in FIG. 2 (a), an air bag device is proposed wherein the air bag device has a conventional air bag (hereinafter, the air bag shown by long and short dash lines is called by "main bag") and an air bag formed in a ring shape to cover a periphery of the steering wheel (hereinafter, the air bag formed in a ring shape and disposed at a periphery of the main bag is called by "sub bag") and the both air bags are deployed (See Journal of Technical Disclosure published by Japan Institute of Invention and Innovation, Technical Disclosure No. 88-15251, Published Unexamined Utility model No. 1989-122349).
In the air bag device disclosed in the Journal of Technical Disclosure No. 88-15251, as shown in FIG. 2(a) and FIG. 2(b), the sub bag 61 is folded and accommodated in a hollow rim 62 of the steering wheel 70 and gas for inflation and deployment is introduced into the sub bag 61 through a spoke 63 acting also as a gas pipe as shown by the arrow. The hollow rim 62 has a tear line 64 formed at a predetermined position thereof. As the gas is introduced into the sub bag 61 to apply an inner pressure, the tear line 64 breaks and portions 62a of the hollow rim 62 is expanded in a direction of the arrow B, then the sub bag 61 accommodated inside the hollow rim 62 expands like a rush. At the same time, the main bag 66 expands and deploys so as to prevent the occupant moving in a direction of the arrow A from bumping against the steering wheel 70 and to protect the occupant's head and chest from an impact.
However, a considerable capacity in the hollow rim 62 is necessary for folding and accommodating the sub bag 61 in the hollow rim of the steering wheel 70. The diameter of the rim 62 becomes wide, so that the grip size becomes big and an operational feeling for steering becomes inferior.
Because the rim 62 is a portion which the driver always holds to steer, the rim 62 should have rigidity and strength not to break even if the rim is griped hard. On the other hand, the tear line formed on the periphery of the rim 62 should be formed as a weak part to easily break when the internal pressure is applied by introducing gas. Actually, it is quite difficult to make such a rim 62 structured to be compatible as mentioned above.
Furthermore, even if the rim is designed to overcome the above conditions, it takes time to fold and accommodate the sub bag 61 in the rim 62 and to mount the gas pipe and the like. Therefore, the whole air bag device becomes quite expensive.
It is an object of the present invention to solve the problems of the prior art as mentioned above and to provide an air bag device having a sub bag with reasonable cost and simple structure.